Bitumen is a heavy type of crude oil that is often found in naturally occurring geological materials such as tar sands, black shales, coal formations, and weathered hydrocarbon formations contained in sandstones and carbonates. Bitumen may be described as a flammable brown or black mixture of tarlike hydrocarbons derived naturally or by distillation from petroleum. Bitumen can be in the form of a viscous oil to a brittle solid, including asphalt, tars, and natural mineral waxes. Bitumen is often referred to in the industry as a naturally occurring viscous mixture, composed mainly of hydrocarbons heavier than pentane (may contain sulfur compounds), and in its naturally occurring viscous state will not flow to a well.
Substances that include bitumen may be referred to as bituminous, e.g., bituminous coal, bituminous tar, or bituminous pitch. At room temperature, the flowability of bitumen is much like cold molasses. Bitumen may be processed to yield oil and other commercially useful products, primarily by cracking the bitumen into lighter hydrocarbon material.
As noted above, tar sands represent one well known source of bitumen. Tar sands typically include bitumen, water, and mineral solids. The mineral solids may include inorganic solids such as coal, sand, and clay. Tar sand deposits can be found in many parts of the world, including North America. One of the largest North American tar sands deposits is in the Athabasca region of Alberta, Canada. In the Athabasca region, the tar sands formation can be found at the surface, although it may also be buried two thousand feet below the surface overburden or more.
Tar sands deposits can be measured in barrels of equivalent oil. It is estimated that the Athabasca tar sands deposit contains the equivalent of about 1.7 to 2.3 trillion barrels of, oil. Global tar sands deposits have been estimated to contain up to 4 trillion barrels of oil. By way of comparison, the proven worldwide oil reserves are estimated to be about 1.3 trillion barrels.
The bitumen content of tar sands may vary from approximately 3 wt % to 21 wt %, with a typical content of approximately 12 wt %. The remainder is water and mineral matter such as sand and clay.
The first step in deriving oil and other commercially useful products from bitumen is to separate the bitumen from the carrier material. In the case of tar sands, this may include separating the bitumen from the mineral solids and other components in the tar sands.
One method for extracting bitumen from tar sands is with a hydrocarbon solvent. The solvent is mixed with tar sand and dissolves the bitumen. The solvent phase is separated from mineral matter and other materials, which form the tailings. In this way, the process can successfully extract most of the bitumen from the tar sands.
One of the challenges associated with using a hydrocarbon solvent is separating the solvent from the tailings. Many government authorities severely limit the amount of hydrocarbon solvent that can be discharged with the tailings. Meeting this requirement can be difficult.